We have to save the value per account and contact, because otherwise
it could lead to problems if a jid is added to more than one account.

As key this uses a string in the form of 'Account-BareJid'.

The config option group 'contacts' is not used because there are values
like 'speller_language' that make more sense to set on a Jid basis, rather than a
Account-Jid basis.

Treat an empty config value or no config value as 'disabled', instead
of writing a config value of 'disabled'. This has the benefit that we
dont have to write config values for contacts were we dont use encryption.

Because of the new build process this has become obsolete
we can now log on windows with a simple

´Gajim.exe > log.txt 2>&1´

This is a regression from !96

Zeroconf: SSL_ERROR_* has been moved to ssl module

Closes #8625

See merge request !100

fixes #8625

Switch to using MSYS2 for Windows build

See merge request !99

install css style file

See merge request !97

New Encryption Plugin API

See merge request !96

- Log status is a feature that only works with xep-0136 which nobody uses anymore
- Even then we can only trust in the server/user to not log the session
- We should not imply that a client could control if messages are logged on the server or the other end,
 especially as this is about encryption and security we should be as accurate as possible

- The lock image is only shown if a encryption was sucessfully activated, so the enabled flag is unnecessary

- Add extension points when receiving/sending a message
- Add extension point for setting the lock image
- Add extension point after clicking the send button
- Add extension point when typing
- Add a new menu button to choose the desired encryption
- Extend the PluginManager to hold a list of encryption plugins

appdata: remove zero width space (U+200B) add by mistake

See merge request !95

add AppData file

Closes #8174

See merge request !94

fixes #8174

Use account hostname for STUN server discovery

See merge request !93

Use the account hostname instead of the target hostname of the
_xmpp-client._tcp SRV resource record for STUN server discovery.
Otherwise, discovery fails if both hostnames are different.

If the user had an empty `file_transfer_proxies` config setting
no proxies were used. As we discover the default server proxy ourself the
user should not have to write it to his config setting to make use of it.

Add support for systemd's networkd

See merge request !91

https://xmpp.org/extensions/xep-0184.html#what tells us that we
SHOULD NOT impute any meaning to the fact that we did not receive an ack message

- We want to send requests also to offline contacts.
- The XEP is wide spread chances are high that a contact supports it.
- It gets really complicated, when we want to guess if a offline contact supports receipts

- 'received'-Carbons from ourself, because we either received
   the message directly or got a 'sent'-Carbon about it
-  Messages from our own full jid, this can happen when we send
   a Message to ourself and no other resource is online.